Huh...I wonder if they have any guesses as to the duration of the cycles?
It seems to me that their margin of 100 million years between the deposition of the rocks they sampled, and the stabilization of the atmosphere by cyanobacteria, is a terribly small increment of time compared to the 2.5-2.65 billion year age of the rocks...the individual cycle layers must span periods close to their capability to measure them!

"There has been an alarming increase in the number of things I know nothing about."
-Ashleigh Ellwood Brilliant